The present disclosure relates generally to medical methods and devices. More particularly, the present disclosure relates to methods, systems and devices to treat carotid artery disease.
Carotid artery disease usually consists of deposits of plaque which narrow the internal carotid artery ICA at or near the junction between the common carotid artery and the internal carotid artery. These deposits increase the risk of embolic particles being generated and entering the cerebral vasculature, leading to neurologic consequences such as transient ischemic attacks TIA, ischemic stroke, or death. In addition, should such narrowings become severe, blood flow to the brain is inhibited with serious and sometimes fatal consequences.
Two principal therapies are employed for treating carotid artery disease. The first is carotid endarterectomy CEA, an open surgical procedure which relies on clamping the common, internal and external carotid arteries, surgically opening the carotid artery at the site of the disease (usually the carotid bifurcation where the common carotid artery divides into the internal carotid artery and external carotid artery), dissecting away and removing the plaque, and then closing the carotid artery with a suture. The risk of emboli release into the internal and external arteries is minimized. During the procedure while the artery is opened, all the carotid artery branches are clamped so particles are unable to enter the vasculature. The arteries are debrided and vigorously flushed before closing the vessels and restoring blood flow. Because the clinical consequence of emboli release into the external carotid artery is less significant, the common carotid and external carotid arteries are usually unclamped first, so that any embolic particles which remain in the bifurcation or in the common carotid artery are flushed from the common carotid artery into the external carotid artery. As a last step, the internal carotid artery clamp is opened to restore arterial flow throughout the carotid circulation.
The second procedure, carotid artery stenting CAS, relies on deployment and expansion of a metallic stent across the carotid artery stenosis, typically at or across the branch from the common carotid artery into the internal carotid artery, or entirely in the internal carotid artery, depending on the position of the disease. Usually, a self-expanding stent is introduced through a percutaneous puncture into the femoral artery in the groin and up the aortic arch into the target common carotid artery. If deemed necessary, a balloon dilatation of the stenosis is performed before the stent is inserted, to open the lesion and facilitate the placement of the stent delivery catheter and of other devices. In the majority of instances, a balloon dilatation is performed on the stenosis after the stent is placed, to optimize the luminal diameter of the stented segment. Usually, a guide wire remains in place across the stenosis during the entire intervention of the stenosis to facilitate the exchange of the various devices for pre-dilatation, stent delivery, and post-dilatation. The guide wire remains in place until a final angiogram confirms an acceptable outcome.
In carotid stenting procedures, adjunct embolic protection devices are usually used to at least partially alleviate the risk of emboli. One category of embolic protection devices is distal filters. These filters are positioned in the internal carotid artery distal to the region of stenting, prior to balloon dilatation and stent deployment. The filter is intended to capture the embolic particles to prevent passage into the cerebral vasculature. After the intervention is complete, the filter is retrieved from the vasculature.
Another category of embolic protection is flow occlusion or reversal in the internal carotid artery to prevent embolic debris entering the cerebral vasculature during the procedure. One example of flow occlusion is the method described by Henry et al. (1999) “Carotid stenting with cerebral protection: First clinical experience using the PercuSurge GuardWire System” J. Endovasc. Surg. 6:321-331, which is incorporated by reference herein in its entirety, whereby an occlusion balloon is placed in the ICA distal to the region of stenting and then inflated to occlude flow and prevent embolic particles from travelling to the brain. Prior to deflation of the distal occlusion balloon, a separate aspiration catheter is introduced into the treatment site to remove embolic debris.
In an alternate method proposed by Reimers and Coppi (Reimers et al. (2005) “Proximal endovascular flow blockage for cerebral protection during carotid artery stenting: Results from a prospective multicenter registry” J. Endovasc. Ther. 12:156-165, the common carotid artery and external carotid artery are occluded proximal to the treatment site using a dual balloon catheter inserted transfemorally to the target carotid artery. The distal-most balloon on the catheter is positioned in the external carotid artery and the proximal-most balloon is positioned in the common carotid artery. An opening in the catheter between the two balloons is used to deliver the interventional devices into the target internal carotid artery. During periods of the intervention and at the end of the intervention prior to establishing forward flow in the internal carotid artery, aspiration is performed between the two balloons to remove embolic debris.
In a reverse flow embolic protection method, an arterial access cannula is connected to a venous cannula in order to establish a reverse or retrograde flow from the internal carotid artery through the arterial cannula and away from the cerebral vasculature. Flow in the common carotid artery is occluded, typically by inflating a balloon on the distal tip of the cannula. Flow into the external carotid artery can also be occluded, typically using a balloon catheter introduced through the cannula. After such reverse or retrograde flow is established, the stenting procedure can be performed with a greatly reduced risk of emboli entering the cerebral vasculature.
All of the methods above rely on transfemoral access to position the embolic protection and interventional devices including the carotid artery stent. This access approach is well known for coronary interventions. However, in many patients, this approach to the carotid artery can involve traversing tortuous anatomy and/or diseased vessels, often leading to prolonged procedure times and can itself be a source of embolic complications. An alternate, transcervical access to the carotid arteries has been proposed for CAS procedures, either a direct, surgical access or percutaneous access to the cervical carotid artery, sometimes using distal filters. A transcervical reverse flow method utilizing a surgical approach can also be used. Such an approach eliminates complications associated with gaining transfemoral endovascular access to the common carotid artery, and allows the possibility of much shorter and potentially larger profile and/or more rigid interventional stent delivery devices. In addition, most relevant to the reverse flow methods, the shorter length reduces the flow resistance and thus increases the level of reverse flow achievable. This increased reverse flow reduces the need to occlude the external carotid artery by reducing the potential flow from the external carotid artery antegrade to the internal carotid artery during common carotid artery occlusion in the case of an external carotid artery to internal carotid artery pressure gradient. The elimination of the external carotid artery occlusion balloon greatly reduces the complexity, risk and potential complications of the procedure.
The transcervical access offers a potentially safer and more rapid access to carotid artery interventions. However, this access can have some drawbacks. One is that there is limited amount of sheath length that can be inserted. If the access sheath is inserted into the area of the bifurcation, it can interfere with deployment of the stent at the target site. In addition, the tip of the sheath can contact diseased material and cause embolic particles to be generated at the target site before any embolic protection system is employed. There is a need to limit the length of sheath insertion. However, if the access sheath is limited in the amount it can be inserted into the artery, there is a greater risk of inadvertent sheath removal during the procedure, especially as interventional devices are inserted and removed from the sheath creating forces on the sheath. Thus, there is also a need for features on the sheath which aid in prevention of over insertion and of sheath retention.
During a CAS procedure, there are periods of increased risk of release of embolic debris. These periods have been documented in studies using Transcranial Doppler (TCD) technology to measure the passage of embolic debris in the cerebral arteries during the CAS procedure. One of these periods is when a device, for example a dilatation balloon or stent delivery device, crosses the stenosis. Another example is when the post-stent dilatation balloon is deflated (presumably releasing embolic particles that have been generated during the dilatation). For reverse or static flow protocols where the common carotid artery is occluded, there is also an elevated risk of embolic particles when the common carotid artery is un-occluded. For these reasons, it would be desirable to provide methods and devices which would enable a CAS intervention with a reduction in the number of devices required to cross the stenosis. It would further be desirable to provide methods and devices which can offer augmented protection from embolic events during critical periods of intervention.
None of the cerebral protection devices and methods described offer protection after the CAS procedure. However, clinical and sub-clinical cerebral ischemia has been measured up to 48 hours post stent procedure. During CEA, flushing at the end of the procedure while blocking flow to the internal carotid artery can help reduce procedural and post-procedural emboli generation. Studies which have compared CAS and CEA procedures have documented a significantly higher level of micro-ischemic events during CAS procedures as measured by diffusion-weighted magnetic resonance imaging (DW-MRI). This suggests that the methods used to remove embolic debris and prevent embolic generation are more effective in CEA than in CAS procedures. It can be advantageous to provide a means to flush and/or aspirate the treated area during a CAS procedure to similar effect as is done in a CEA procedure, and further to isolate the internal carotid artery during removal of the common carotid artery occlusion so that any potential debris proximal to the common carotid artery occlusion or in the treatment zone is forward flushed via arterial blood flow into the external carotid artery before arterial flow is reestablished into the internal carotid artery.